Existing phased array antennas include a wide variety of configurations for various applications, such as satellite reception, remote broadcasting or military communication. The desirable characteristics of low cost, light-weight, low profile and mass producibility are provided in general by printed circuit antennas. The simplest forms of printed circuit antennas are microstrip antennas wherein flat conductive elements are spaced from a single essentially continuous ground element by a dielectric sheet of uniform thickness. An example of a wideband phased array antenna is disclosed in U.S. Pat. No. 6,512,487 to Taylor et al., which is incorporated herein by reference and is assigned to the current assignee of the present invention.
An alternative to microstrip antennas is slotted antennas. A slotted phased array antenna may also be used for communication systems such as identification of friend/foe (IFF) systems, personal communication service (PCS) systems, satellite communication systems and aerospace systems, which require such characteristics as low cost, light weight, low profile and a low sidelobe.
The bandwidth and directivity capabilities of a slotted phased array antenna, however, can be limiting for certain applications. While the use of magnetically coupled slotted antenna elements can increase bandwidth, obtaining this benefit presents significant design challenges, particularly where maintenance of a low profile and broad beamwidth is desirable. Also, the use of slotted antenna elements can improve directivity in a given direction by providing a predetermined scan angle. However, utilizing a slotted phased array antenna presents a dilemma. The scan angle can be increased if the slotted antenna elements are spaced closer together, but closer spacing can increase undesirable coupling between slotted antenna elements, thereby degrading performance.
Increasing the bandwidth of a slotted phased array antenna with a wide scan angle is conventionally achieved by dividing the frequency range into multiple bands. This approach results in a considerable increase in the size and weight of the antenna. For example, U.S. Pat. No. 5,648,786 to Chung et al. discloses a wideband slotted phased array antenna. The antenna in the '786 patent is a periodic slot array antenna comprising a plurality of arrays. The arrays comprise a plurality of conductive cavities adjacent to one another with varying conductive cavity sizes in accordance with a log-periodic scale. The bandwidth of the antenna is extended since several varying size cavities and slots are used, but at the expense of the antenna's overall size and weight.